%0 Journal Article %T Static and Dynamic User Portraits %A Ko-Hsun Huang %A Yi-Shin Deng %A Ming-Chuen Chuang %J Advances in Human-Computer Interaction %D 2012 %I Hindawi Publishing Corporation %R 10.1155/2012/123725 %X User modeling and profiling has been used to evaluate systems and predict user behaviors for a considerable time. Models and profiles are generally constructed based on studies of usersĄŻ behavior patterns, cognitive characteristics, or demographic data and provide an efficient way to present usersĄŻ preferences and interests. However, such modeling focuses on usersĄŻ interactions with a system and cannot support complicated social interaction, which is the emerging focus of serious games, educational hypermedia systems, experience, and service design. On the other hand, personas are used to portray and represent different groups and types of users and help designers propose suitable solutions in iterative design processes. However, clear guidelines and research approaches for developing useful personas for large-scale and complex social networks have not been well established. In this research, we reflect on three different design studies related to social interaction, experience, and cross-platform service design to discuss multiple ways of identifying both direct users and invisible users in design research. In addition, research methods and attributes to portray users are discussed. 1. Introduction Understanding target users is considered a basic step towards developing good products and services. In traditional industrial design, marketing, city planning, and environmental design, a wide range of research methods, including surveys, field studies, interviews, and focus groups, have been used with the clear purpose of identifying target audiencesĄŻ preferences and needs [1¨C4]. In system and software development, usability evaluation and user-centered design methods, such participatory design, contextual inquiry, or ethnographic techniques, have also been well accepted and applied to better understand end usersĄŻ knowledge background, behaviors, cognitive processes, and requirements [5¨C7]. To support rapid IT development and iterative design processes, it has become important to have clear images and models to represent end users: ideally models which can be reused and reapplied in the development of different products and services [8]. In software engineering, user modeling has focused on having an internal representation of users, which includes information such as background knowledge, preferences, and the ways that users interact with systems [9¨C11]. This type of user modeling or profiling can be used to design serious games, educational training, and learning systems or to evaluate systems by simulating different types of users [11¨C13]. Beyond %U http://www.hindawi.com/journals/ahci/2012/123725/